docs: def _sigma_ee_rel(self, gam, eps):
          """
          Eq. A1, A4 of Baring et al. (1999)
          Use for Ee > 2 MeV
          """
          A = 1 - 8 / 3 * (gam - 1) ** 0.2 / (gam + 1) * (eps / gam) ** (
              1.0 / 3.0
          )
  
          return (self._sigma_1(gam, eps) + self._sigma_2(gam, eps)) * A